1. Field of the Invention
The present invention relates to a camera system including: an imaging unit which has an image-taking optical system and an image pickup device; and a main unit which receives image signals from the imaging unit and performs signal processing.
2. Description of the Related Art
There has been proposed a camera system including a main unit and an imaging unit provided with an image-taking optical system and an image pickup device, which can take an image while maximizing the utilization of the image-taking function of the imaging unit by detachably attaching the imaging unit to the main unit. This type of camera systems may take images while freely changing a focal length, a focus range, etc. by selecting an imaging unit in a manner similar to the use of a conventional interchangeable lens, or may take color images by using an image pickup device having various color filters.
In order to put this type of camera systems into wide spread use in the future, it is necessary to design such a camera system that allows any of imaging units to be attached to a main unit to take images. One of techniques for realizing such a design is disclosed in Japanese Patent Application Publication No. 2000-106644 that proposes a main unit equipped with two or more processing means respectively operating for different types of image pickup devices.
The camera system of the above document can perform signal processing by using any one of the processing means provided in the main unit even if any of imaging units is attached to the main unit. In such a camera system however, even if an improper imaging unit (e.g. an imaging unit incompatible with the specification of the main unit, a completely counterfeit unit, etc.) is attached to the main unit, some kind of image processing may be performed by the processing means of the main unit when data of a taken image is sent to the main unit.
In order to address this problem, Japanese Patent Application Publication No. 2001-16498 proposes a camera system whose main unit includes: an identification section that identifies whether an imaging unit is proper or not when it is attached to the main unit; and a restriction section that restricts shooting according to the result of the identification performed by the identification section, thereby preventing an improper imaging unit from being attached to and used with a main unit.
In recent years however, because imaging units are becoming highly intelligent, there is a trend to provide main units with only the function of recording and reproducing images to make them as simple as possible. In the circumstances, providing a main unit with an identification section by employing the technique disclosed in Japanese Patent Application Publication No. 2001-16498 would oppose the trend.
Further, when main units are thus simplified, they can be sold at a low price so that many users can purchase them. Some users may possess various types of main units and select one of them according to the size of an imaging unit, or some users may possess various types of imaging units and borrow a main unit from somewhere according to one of various types of their own imaging units.
Under such circumstances, it is more likely that a proper imaging unit may be attached to an improper main unit rather than an improper imaging unit may be attached to a proper main unit.